Beam addressable file using thin magnetic films of insulators are known in the art. For instance, materials such as gadolinium iron garnets have been used. Also, metals such as MnBi have been used as the storage medium in beam addressable files. General descriptions of these file systems can be found in the following:
1. A. H. Eschenfelder, J. APPL. PHYS., 41, 1372 (1970). PA1 2. J. A. Rajchman, J. APPL. PHYS., 41, 1376 (1970). PA1 3. R. E. McDonald et al., J. APPL. PHYS., 40, 1429 (1969). PA1 4. D. Chen et al. , J. APPL. PHYS., 39, 3916 (1968).
In addition to these materials, stoichiometric MnAlGe has been suggested as a suitable material in a magneto-optic environment. This is a polycrystalline film.
Some non-magnetic amorphous materials have been used in beam addressable file environments, as can be seen by referring to U.S. Pat. No. 3,530,441. These amorphous materials are "ovonic-type" materials which do not exhibit magnetic properties. They undergo structural changes when being switched in the beam addressable environment in contrast with the switching which occurs in a magnetic film. Because structural changes (transitions between an amorphous and a crystalline state) are much more destructive on the film itself, magnetic films can be switched many more times than non-magnetic amorphous films in this type of environment.
Amorphous films have an advantage in that they can be placed on any type of substrate and can be adjusted to provide wide composition ranges. Additionally, the requirements relating to polycrystalline grain size which are present with crystalline beam addressable storage material are not present.
More recently, amorphous materials suitable as magnetic medium such as in beam addressable file environments have been disclosed in U.S. Pat. Nos. 3,949,387 and 3,965,463 to Chaudhari, et al. and assigned to International Business Machines Corporation, the assignee of the present application, disclosures of which being incorporated herein by reference.
However, although the amorphous materials disclosed in U.S. Pat. Nos. 3,949,387 and 3,965,463 exhibit magneto-optical properties suitable for their desired use, such materials could stand improvement with respect to certain properties. For instance, increased degree of Faraday rotations would be desirable to facilitate the read out of a file. Other properties needed for a material to be practical as a magnetic medium in a beam addressable system include existence of an atomic magnetic moment, spin orbit coupling, magnetic order, magneto-optic response at the desired wavelength and square loop hysteresis. Accordingly, it is apparent that providing materials capable of satisfying the requirements for beam addressable magnetic storage medium is quite a difficult task.